Ejercicio 8 - Trabajo práctico 2 - 2017

import java.util.Stack;
import java.util.Scanner;

public class TP2E08 {

    public static void main(String[] args) {
        TP2E08 exercise = new TP2E08();
        exercise.execute();
    }

    private void execute() {
        Scanner console = new Scanner(System.in);
        System.out.print("Ingrese una expresión interfija: ");
        String interFixExpression = console.nextLine();
        System.out.println("Expresión posfija: " + toPostFix(interFixExpression));
        console.close();
    }

    private String toPostFix(String interFixExpression) {
        String postFixExpression = "";

        Stack<Character> operators = new Stack<Character>();

        Character c;
        for (int i = 0; i < interFixExpression.length(); ++i) {

            c = interFixExpression.charAt(i);
            if ((c >= '0') && (c <= '9')) {
                postFixExpression += c;
            } else {
                while ((operators.size() > 0) && (precedence(operators.peek()) >= precedence(c))) {
                    postFixExpression += operators.pop();
                }
                operators.push(c);
            }
        }

        while (operators.size() > 0) {
            postFixExpression += operators.pop();
        }

        return postFixExpression;
    }

    private int precedence(Character operator) {
        switch(operator) {
        case '+' :
            return 1;
        case '-' :
            return 1;
        case '*' :
            return 2;
        case '/' :
            return 2;
        default :
            return 3;
        }
    }
}